1. Field of the Invention
This invention relates to a method for controlling the rotation of an engine, in particular, an engine of a construction vehicle such as, for example, a power shovel or the like, and a system for carrying out the method, and more particularly to an auto-decelerator system.
Construction vehicles such as power shovels etc. are operated for excavation and earth moving etc. under the condition that engines are running at their full speeds. Between the excavating and earth moving operations, there is a time of suspension or out of operation such as waiting time for dump trucks. During such a time of suspension of operation, it is desirable to run the engine idle in order to prevent the occurrence of noise and practice economy in fuel consumption. It is, however, trouble-some for operators to shift the fuel control lever to its idling position each time of suspension of operation. For this purpose, in the engine fuel control system there is provided an auto-decelerator device arranged, when the operation is suspended and all actuators are rendered inoperative, to detect this condition to allow the engine's fuel control system to be operated under idling condition irrespective of the fuel control lever located at its full speed running position.
2. Description of the Prior Art
The construction vehicles such as power shovels etc. have been disadvantageous in that when the number of revolutions of the engine is set by means of a fuel control lever, the engine continues to run at the same number of revolution even when excavating and earth moving operation are suspended thereby generating noise and increasing fuel consumption.
To eliminate the above-mentioned disadvantage, the applicant of the present invention developed an engine control system for a construction vehicle such as a shovel loader etc. as disclosed in Japanese Utility Model Provisional Publication No. 58-156138 arranged such that pressurized fluid is supplied into a running control circuit and an implement control circuit by at least two hydraulic pumps driven by the engine, and the number of revolutions of the engine is set by means ofaa governor control lever adapted to be operated by a fuel control lever, characterized in that said governor control lever is provided with a hydraulic cylinder for driving adapted to hold the governor control lever at its idling position (that is; low speed running position) when the hydraulic pump is under no load condition and also to move the governor control lever to its full speed running position as the load on the hydraulic pump increases.
This engine control system, however, utilizes the fluid pressure delivered by the hydraulic pump to urge the governor control lever in the direction of full speed rotation, and so it is subjected to the influence by changes in manipulated variable produced by the fluid pressure force thus causing an undesirable low speed (idling) condition of the engine. For example, when an implement is lowered, the lowering of the implement by its dead weight gives an adverse affect so that a sufficient rise in fluid pressure cannot be obtained. This is true in the case of turning of the turning unit by its inertia. Consequently the fluid pressure required to urge the governor control lever in the direction of full speed rotation will drop thus causing a movement of the lever towards idling position by a resilient force of a spring thereby reducing the number of revolutions of the engine. Furthermore, since the fluid pressure required to urge the governor control lever in the direction of full speed rotation becomes unavailable when all the operating levers are shifted to their neutral positions, the number of revolutions of the engine will drop immediately thus causing a time lag in operation when excavation and earth moving operations are made successively, a deterioration in operating performance and repeated increase in number of revolutions of the engine thereby generating noise.
The present invention has been developed in view of the above-mentioned circumstances, and has for its aspect to provide a method and a system for controlling an engine of a construction vehicle such as a shovel loader etc., characterized in that it comprises a hydraulic pump for exclusive use in controls of the governor without having to use fluid under pressure delivered from hydraulic pumps for use in implements, the arrangement being made such that changes in fluid pressure force due to operation of the implement do not give adverse affect to the control of the governor, the fluid under pressure delivered from the hydraulic pump for controlling the governor is controlled by means of a solenoid control valve to thereby extend and contract the piston rod of a decelerator cylinder, said solenoid control valve being adapted to be changed over in electrical response to the positions of implement operating levers, and said governor can be controlled automatically between full speed rotating condition and idle running condition.
Another aspect of the present invention is to provide a method and a system for controlling an engine of a construction vehicle such as a shovel loader etc., characterized in that it comprises a single timer so that a governor control lever is held at its full speed running position for a few seconds, for example, about four seconds after all operating levers have been returned to their neutral positions, respectively, and then automatically moved to its idling position.
A further aspect of the present invention is to provide a method and a system for controlling an engine of a construction vehicle such as a shovel loader etc., characterized in that it comprises two timers so that a governor control lever is moved towards its idling position immediately after all operating levers have been returned to their neutral positions thus causing a temporary small extent reduction in the number of revolutions of the engine, and then moved again to its idling position to enable a further large extent reduction in the number of revolutions to be obtained.
To achieve the above-mentioned first and second aspects, according to the present invention, there is provided a method of controlling an engine provided with an auto-decelerator system in a construction vehicle such as a shovel loader etc., characterized in that the auto-decelerator system is actuated a few seconds after all operating levers have been returned to their neutral positions, respectively, thereby allowing the number of revolutions of the engine to be reduced from those in the full speed condition to those in the idling speed condition.
Further, to achieve the above-mentioned third aspect, according to the present invention, there is provided a method for controlling an engine provided with an auto-decelerator system in a construction vehicle such as a shovel loader etc., characterized in that the auto-decelerator system is temporarily actuated immediately after all operating levers have been returned to their neutral positions, respectively, thereby causing a small extent reduction in the number of revolutions of the engine, and after allowing the engine to run under such a condition for a predetermined period of time, the auto-decelerator system is actuated again to reduce the number of revolutions of the engine to those in the idling speed condition.
Still further, to achieve the above-mentioned first and second aspects, according to the present invention, there is provided an auto-decelerator system comprising a mechanism for mechanically transmitting the manipulated variable produced by the fuel control lever through the intermediary of a loose spring to the governor of the engine; a hydraulic actuator connected between the loose spring of the manipulated variable transmitting mechanism and the governor, the hydraulic aotuator being adapted, when actuated, to return the governor to its idling position; means for detecting the inoperative condition of all operating levers in the construction vehicle, and a timer circuit device for actuating said hydraulic actuator when the inoperative condition of said operating levers has been detected continuously for more than a predetermined period of time.
Further, to achieve the above-mentioned third aspect, according to the present invention, there is provided an auto-decelerator system comprising a mechanism for mechanically transmitting the manipulated variable of the fuel control lever through the intermediary of a loose spring to the governor of the engine; a hydraulic actuator connected between the loose spring of the manipulated variable transmitting mechanism and the governor, the hydraulic actuator being adapted, when actuated, to return the governor to its idling position; means for detecting the inoperative condition of all operating levers of the construction vehicle, and a timer circuit device including a first timer adapted to detect immediately the inoperative condition of the operating levers to actuate temporarily the hydraulic actuator and a second timer adapted to activate the hydraulic actuator again a predetermined time after the first timer is rendered off.
In the above-mentioned auto-decelerator system, the operating levers comprise implement operating levers and running operation control levers, the implement operating levers serving to actuate proportional pilot control valves adapted to control the fluid pressure supplied by variable displacement pumps into implement operating hydraulic actuators, and detection of the inoperative condition of the implement operating levers is made by means of a pressure switch adapted to detect the pressure of the fluid discharged through the proportional pilot control valves.
Further, in the above-mentioned auto-decelerator system, te hydraulic actuators each comprise a decelerator cylinder fixedly secured to the side of the bottom thereof which has a pressure chamber formed therein and including, on the head side thereof, a piston rod connected through a york having an elongated hole formed therein to the manipulated variable transmitting mechanism, and a solenoid valve adapted to receive a signal from the controller device thereby supplying the fluid under pressure delivered by a hydraulic pump driven by the engine and which is independent from the implement operating hydraulic pump into the pressure chamber of the decelerator cylinder, the arrangement being made such that, when the hydraulic actuator is under inoperative condition, the movement of said transmitting mechanism caused by the manipulated variable of the fuel control lever is absorbed by the elongated hole of the york so that no influence is given to the operation of the fuel control lever, whilst when the hydraulic actuator is under operating condition, the movement of the transmitting mechanism is restricted by one end of the elongated hole of the yoke.
The above and many other advantages, features and additional objects of the present invention will become apparent to those versed in the art upon making reference to the following detailed description and accompanying drawings in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example.